Various techniques and systems have recently been developed to visualize the anatomy of vascular occlusions by using intravascular ultrasound (IVUS) imaging. IVUS techniques are catheter based and provide a real-time sectional image of the arterial lumen and the arterial wall. An IVUS catheter includes one or more ultrasound transducers at the distal tip of the catheter by which images containing cross-sectional information of the artery under investigation can be determined. IVUS imaging permits visualization of the configuration of the obstructing material and, in varying degrees, the boundaries of the intimal and medial layers of the arterial wall.
One common type of IVUS imaging catheter system typically includes an arrangement in which a single transducer at the distal end of the catheter is rotated at high speed (up to about 2000 rpm) to generate a rapid series of 360-degree ultrasound sweeps. Such speeds result in generation of up to about thirty images per second, effectively presenting a real-time image of the diseased artery.
The transducer is mounted on the end of a drive shaft or cable that is connected to a motor drive at the proximal end of the catheter. The rotating transducer is housed within a sheath that does not interfere with the ultrasound and protects the artery from the rapidly spinning drive shaft. Thus, an IVUS imaging (or “sensing”) catheter may be advanced to the region of an occlusion using conventional angiographic techniques and then may be operated to provide real-time sectional images of the vascular lumen in the arterial wall, including the occluding material and intimal and medial layers of the artery wall. Other types of catheter-based systems for use in visualizing the internal anatomy of body portions implementing sheath-enclosed movable sensing/imaging elements disposed on elongated drift shaft structures are also known, including photo-acoustic, optical coherence tomography, phased array/multiple transducer, and spectroscopic systems.
Medical sensing catheters of these representative types comprise a tubing assembly through which the drive cable movably extends, the tubing assembly typically including a sheath insertable into the patient and having a proximal end fixed to a telescope section which permits the drive cable, and thus the sensor, to be selectively moved though the patient's body via the interior of the inserted sheath which remains stationary in the patient's body. The telescope section comprises a tubular outer catheter or telescope member, to the distal end thereof the proximal end of the sheath is anchored. The telescope section also has a tubular inner catheter or telescope member which telescopes into the interior of the outer telescope member through its proximal end and is movable through the interior of the outer telescope member between retracted and extended positions relative to the outer telescope member. The drive cable is secured to the inner telescope member for longitudinal movement therewith relative to the outer catheter member.
Distal movement of the inner telescope member toward its retracted position distally pushes the drive cable and the sensor through the sheath, and proximal movement of the inner telescope member toward its extended position pulls the drive cable and the sensor back through the sheath. When the inner telescope member is moved to its extended position a portion of the drive cable extending through the interior of the outer catheter member between the distal end of the outer telescope member and the distal end of the inner catheter member is substantially unsupported and unconstrained within the telescope section.
In response to a subsequent movement of the inner telescope member distally toward its retracted position the exposed, unsupported portion of the drive cable may undesirably be caused to buckle within the telescope section, thereby hindering a desired distal advancement of the drive cable through the sheath and potentially damage the cable. A previously proposed solution to this potential drive cable buckling problem has been to position a separate reinforcing structure within the telescope section to support the portion of the drive cable extending through the telescope section when the inner telescope member is moved away from its retracted position.
This previously proposed drive cable supporting technique, however, has proven to be less that wholly satisfactory because it requires the provision and installation in the overall catheter assembly of at least one additional component, thereby undesirably increasing the catheter assembly cost, complexity and manufacturing time. As may be readily seen from the foregoing, a need exists for an improved solution to the above-described catheter drive cable buckling problem. It is to this need that the present invention is primarily directed.